The present invention relates to a hydrogen storage alloy electrode which employs, as an active material, a hydrogen storage alloy capable of electrochemically absorbing and desorbing hydrogen in a reversible manner.
Electrodes employing as an active material a hydrogen storage alloy capable of absorbing and desorbing hydrogen in a reversible manner have a larger theoretical energy density compared to cadmium electrodes. Also, electrodes that employ such hydrogen storage alloy are not susceptible to deformation and subsequent formation of dendrites, which is a problem with zinc electrodes. These advantageous properties, as well as the promise of a longer service life and a reduction in the environmental concerns inherent in cadmium-containing electrode/batteries, have encouraged research into developing alloys suited for hydrogen storage alloy electrodes, and particularly negative electrodes for alkaline storage batteries.
Conventional alloys for hydrogen storage alloy electrodes are typically prepared through either an arc melting process, an induction heating melting process, or some similar process. The hydrogen storage alloys currently used for electrodes are La (or Mm)--Ni system multi-element alloys (wherein Mm (misch metal) is a mixture of rare-earth elements). These multi-element alloys are classified as an AB.sub.5 type (wherein A is La, Zr, Ti or an element with a affinity for hydrogen, and B is Ni, Mn, Cr or any other transition metal with a small affinity for hydrogen).
Another alloy having larger hydrogen storing capability than the AB.sub.5 type is a Ti--V system hydrogen storage alloy. For example, hydrogen storage alloy electrodes employing a Ti.sub.x V.sub.y Ni.sub.z alloy are known in conventional. See, e.g., Japanese Laid-Open Patent Publication Nos. 6-228699, 7-268513, and 7-268514.
The La (or Mm)--Ni system multi-element alloy, however, nearly uses the whole theoretical capacity, so there is little probability of drastic capacity increase.
On the other hand, electrodes made from the Ti--V system hydrogen storage alloy have a larger discharge capacity than electrodes made from the La (or Mm)--Ni system alloy; however, there is a problem that the discharge capacity is still lower than the theoretical discharge capacity. Also, the electrodes have to achieve improved cycle characteristic and cost reduction.